NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE 39 



stage. By any of these methods the end result is large embryos. Snail 

 embryos from 3 to 15 mm. in height are not uncommon. 



The tunicate Dendrodoa grossularia produces eggs that are 0.25 

 mm. in diameter. 



Although many of the marine invertebrates lay eggs at the begin- 

 ning of summer, preparation for egg laying at this time must take 

 place during the winter. Such preparation consists in the develop- 

 ment of functional eggs and sperm. And this in turn must be pre- 

 ceded, in many instances at least, by the storage of oil during the 

 summer for use in the production of eggs during the winter (see 

 Eualus gaimardi under "Storage of Oil"). 



As soon as the ice goes out there are snail egg capsules in abun- 

 dance. These must have been deposited during spring. The only 

 other alternative is that they were deposited in the fall and develop- 

 ment was slow or delayed until spring. 



Although most of the egg capsules could be identified as to genus, 

 only a few of them could be assigned to their proper species. In sev- 

 eral instances in which the species could be recognized, it was noted 

 that capsules with well-advanced embryos were present as soon as 

 the ice went out and that freshly deposited capsules appeared through- 

 out the summer and as late as the middle or end of October. It is 

 possible that those capsules that were deposited in October were the 

 ones containing well-advanced embryos late in July or early in August. 

 Whether the same individual snail lays eggs more than once a year 

 was not determined. It is possible that a snail that lays eggs in Octo- 

 ber could lay again in June or July provided that during the summer, 

 at the same time it was producing eggs to be laid in October, it could 

 also be storing oil to be used during the winter for producing eggs to 

 be laid in June or July, or that it could find sufficient food during 

 winter to produce eggs. But it seems improbable that any one snail 

 reproduces more than once a year. From the slowness with which 

 gonadal development took place in certain species that could be 

 watched (the shrimp Eualus gaimardi, for instance) it seems doubly 

 improbable that many species of the higher invertebrates, at least, 

 could be capable of reproducing more than once a year. 



Throughout the winter of 1949-50 the larvae of the pteropod Clione 

 limacina were always present in plankton tows. During the entire 

 winter there was no perceptible increase in size of these larvae, but 

 in June larger larvae appeared, and on July 20 larvae 7 mm. long and 

 adults 30 mm. long were taken. The 7-mm. larvae were still using 

 cilia, for the wings were not sufficiently developed for locomotion. 



In some of the pelagic invertebrates, such as jellyfishes, cteno- 



